1. Field of the Invention
The present invention relates to a convex/concave pattern-forming stamp that has convex/concave pattern-forming protrusions formed in a predetermined annular area of a surface thereof, for forming a convex/concave pattern in a resin layer on a substrate surface by being pressed against the resin layer, a method of forming the convex/concave pattern using the convex/concave pattern-forming stamp, and a magnetic recording medium that has data-recording tracks formed thereon using the convex/concave pattern formed according to the convex/concave pattern-forming method.
2. Description of the Related Art
In a process of manufacturing semi-conductor elements or recording media, for example, to form a fine (nanometer-sized) convex/concave pattern in a resin layer on a substrate surface, there has been proposed an imprinting method in which nanometer-sized protrusions/recesses (protrusions) formed on a stamp (mold) are pressed against a resin layer on a substrate surface to thereby transfer convex/concave shapes of the protrusions/recesses to the resin layer (Stephen Y. Chou et al., “Imprint of sub-25 nm Vias and Trenches in Polymers”, Applied Physics Letters (US), vol. 67, No. 21, Nov. 20, 1995, pp. 3114-3116).
In this imprinting method, first, a stamp is prepared which has a surface thereof formed with protrusions/recesses that are nanometer-sized (with a width of 25 nm at the minimum). In this case, the protrusions/recesses of the stamp are formed by drawing a pattern on a silicon substrate having a silicon dioxide layer formed on a surface thereof, using an electron beam lithography device, and then carrying out an etching process using a reactive ion etching (RIE) device. Then, PMMA (polymethyl methacrylate) as a resin material is applied to the silicon substrate surface by a spin coating method to form a resin layer having a thickness of 55 nm. Subsequently, the stamp, the substrate, and the resin layer are heated such that the temperatures of the stamp, the substrate, and the resin layer become equal to a temperature (e.g. 200° C.) not lower than 105° C. which is the glass transition point of PMMA, whereafter the protrusions/recesses of the stamp are pressed against the resin layer with a pressure of 13.1 MPa (1900 psi). After allowing the stamp, the substrate, and the resin layer to be cooled down to room temperature, the stamp is separated from the resin layer. Thus, the convex/concave shapes of the protrusions/recesses of the stamp are transferred to the resin layer, whereby a nanometer-sized convex/concave pattern is formed in the resin layer.
On the other hand, there has been proposed a discrete track-type magnetic recording medium (hereinafter also simply referred to as “the magnetic recording medium”) 91 having a plurality of data-recording discrete tracks (hereinafter simply referred to as “the discrete tracks”) 92, 92, . . . formed in a track-forming area 102 on a surface of a disk-shaped substrate 101 (magnetic layer 112) as shown in FIG. 21. In the magnetic recording medium 91, the discrete tracks 92 are magnetically separated from each other by a plurality of concentric annular grooves formed in a resin layer of the disk-shape substrate 101 such that they have a convex/concave pattern, according to the imprinting method described above. The convex/concave pattern used for forming the discrete tracks 92 of the magnetic recording medium 91 is formed using a stamp 41 having nanometer-sized protrusions 51, 51, . . . formed in an annular area 43 on a surface thereof as shown in FIGS. 17 and 18. The annular area 43 is defined, as shown in FIG. 19, to have the same size as the track-forming area 102 of the disk-shaped substrate 101. In forming the convex/concave pattern using the stamp 41, according to the imprinting method described above, after forming a resin layer 103 on the surface of the disk-shaped substrate 101 comprised of, for example, a disk 111 made of glass, the magnetic layer 112, and a metal layer 113, the protrusions 51, 51, . . . of the stamp 41 are pressed against the resin layer 103 as shown in FIG. 19. As a result, as shown in FIGS. 19 and 20, the convex/concave pattern is formed in a convex/concave pattern-forming area 104 of the resin layer 103 corresponding to the annular area 43 of the stamp 41.
The present inventors have studied the above-descried conventional stamp 41, and found the following problems: As shown in FIG. 19, the stamp 41 has the protrusions 51, 51, . . . formed only in the annular area 43 which is defined to have the same size as the track-forming area 102. The stamp 41 also has an outer area 44 and an inner area 45 located radially outward and inward of the annular area 43, respectively, as shown in FIGS. 17 to 19, and neither of the two areas 44 and 45 is formed with any protrusions 51, which bring about the following inconveniences: since no protrusions are formed in the outer and inner areas 44 and 45, when the stamp 41 is pressed against the resin layer 103, there occurs concentration of pressure on an outer peripheral portion 104b (see FIG. 20) of the convex/concave pattern-forming area 104 and an inner peripheral portion 104c (see FIG. 20) of the same. For this reason, the depth of recesses (height of protrusions) formed in the outer and inner peripheral portions 104b and 104c of the convex/concave pattern-forming area 104 becomes larger than the depth of recesses (larger than the height of protrusions) formed in a central portion 104a of the convex/concave pattern-forming area 104, which makes the recesses non-uniform in depth. Further, since the pressure is concentrated on the outer and inner peripheral portions 104b and 104c of the convex/concave pattern-forming area 104, the convex/concave pattern is deformed in the outer and inner peripheral portions 104b and 104c. Moreover, there arises the problem that portions (resin material) of the convex/concave pattern in the outer and inner peripheral portions 104b and 104c adhered to the corresponding protrusions 51 of the stamp 41 are peeled off the substrate when the stamp 41 is separated from the resin layer 103. Therefore, the magnetic recording media 91 manufactured using the convex/concave pattern are formed with the discrete tracks 92 non-uniform in height (i.e. depth of the grooves separating the discrete tracks 92), and/or suffer from deformed or lost discrete tracks 92 in the outer and inner peripheral portions of the track-forming area 102, which can cause a recording error in data recording.